1. Field of the Invention
This invention pertains to band saw tools, and in particular to means for adjusting both the tension and tracking alignment of the saw band.
2. Description of the Prior Art
State of the art band saws include an endless blade or saw band entrained about a plurality of spaced rollers or pulleys, all arranged in a common plane. One of the pulleys is motor-driven to move the blade along a path through a work station where a work piece may be positioned to be cut by the moving blade.
When using a band saw of the type described, it is important that proper tension be maintained on the blade, since a minimum amount of tension is required for cutting through a work piece. Conversely, too great a tension applied to the saw band can shorten the life thereof. Further, it is recommended that when the saw band is not in use, the tension thereon be released in order to prevent fatiguing of the saw band, thereby prolonging the life thereof.
Conventionally, in saw band tools of the type described, one of the pulleys supporting the saw band is moved along a common plane, into and out of engagement with the saw band, so as to apply and remove tension on the saw band, respectively. The tension adjustment of the band saw tool usually includes a tension adjusting screw which is manually rotatable to incrementally advance the movable pulley in first and second directions, so as to incrementally increase or decrease tension on the saw band. With this mechanism, tensioning adjustments must be made every time the band saw tool is returned to use, if fatigue of the saw band is to be avoided. Also, adjustments to the saw band tension must be made every time a saw band is replaced. This adjusting operation, using tension adjusting screws and the like can be time consuming, and makes it difficult to accurately provide a predetermined tension on the saw band each time the band saw tool is returned to service.
While the pulleys of the saw band tool are arranged in generally coplanar fashion, the slightest deviation or misalignment of any one pulley from the common plane may cause the saw band to shift in directions transverse to the common plane, so as to become either partially or completely disengaged from the pulleys upon which it is entrained. The ability of the saw band to remain in contact with the support pulleys, and to run steadily along the common plane defined by the support pulleys of the band saw tool is commonly known as "tracking." Any tendency of the saw band to shift laterally with respect to the plane of the pulleys is known as "tracking error." It is generally desirable to eliminate "tracking error" of the saw band so as to maintain the cutting efficiency of the band saw tool, as well as to prolong the life of the saw band. Any "tracking error" attributed to the band saw tool operation, is in fact the cumulative total of "tracking error" produced by all the elements comprising the pulley assembly of the band saw tool.
To minimize "tracking error" in a band saw tool, it is common to mount one of the pulleys about which the saw band is entrained, for adjustable deflection, in that its supporting shaft is made tiltable from directions normal to the common plane. Thus, "tracking error" is dynamically balanced by the tilting adjustment of one pulley, to virtually eliminate lateral shifting of the saw band as it rotates over the plurality of pulleys. To accomplish the latter, in some band saw tools, a major adjustment is required. Other band saw tools include less complicated, but separate adjusting screws for repositioning one of the pulleys on which the blade is mounted.
While the various tensioning and "tracking" mechanisms described heretofore operate successfully for the most part to accomplish their intended results, the provision of separate mechanisms for tensioning and "tracking" of a band saw blade becomes complicated and quite costly. Furthermore, in use, such separate tension and "tracking" mechanisms often make it difficult to eliminate the effect of the adjustment of one mechanism upon the other.